This invention relates to the prevention of grounding accidents for marine vessels. Grounding accidents in the global shipping fleet are a major source of property loss, costing the industry an estimated $400MM annually in insurance liability on global shipping trade of more than $200 billion. U.S. Coast Guard data from the years 1996-1997 indicate that each year, 1170 vessels (towed barges and tugs counted individually) are involved in groundings, in a total of 758 annual incidents on U.S. shipping lanes and waterways.
Despite this significant adverse impact on shipping and commercial fleets worldwide, there exist limited systems for prevention of grounding accidents. Most ships are equipped with sonar to monitor the actual depth of the water beneath the hull. However, this device is a reactive system that provides only a current status and does not protect against anticipated conditions present along the instantaneous track of the boat. This device also requires active monitoring by ship""s crew to detect a hazardous condition. In military operations, use of the sonar may inadvertently betray the boat""s location to enemy vessels.
Vessels may also be equipped with moving map displays that show the vessel""s progress relative to a stored nautical chart. These systems also require the crew to actively monitor the vessel""s progress against the chart and to proactively identify hazardous conditions.
In the aviation industry, various systems have been developed that provide warnings and advisory indications to the pilot of aircraft approaching hazardous terrain. Among such systems are systems generally known as ground proximity warning systems (GPWS) which monitor the flight conditions of an aircraft and provide a warning if flight conditions are such that inadvertent contact with terrain is imminent. Among the flight conditions normally monitored by such systems are radio altitude and rate, barometric altitude and rate, air speed, flap and gear positions. These parameters are monitored and an advisory signal and/or warning signal is generated when the relationship between the parameters is such that terrain impact is likely to occur. Typical examples of such systems are disclosed in U.S. Pat. Nos. 3,715,718; 3,936,796; 3,958,218; 3,944,968; 3,947,808; 3,947,810; 3,934,221; 3,958,219; 3,925,751; 3,934,222; 4,060,793; 4,030,065; 4,215,334; and 4,319,218, all assigned to the same assignee as the assignee of the present invention and hereby incorporated by reference. U.S. Pat. Nos. 5,488,563 and 5,839,080 to Mueller et al. each disclose a controlled flight into terrain alerting system that utilizes a terrain database in conjunction with aircraft dynamics to alert pilots of dangerous proximity to terrain.
However, such systems are designed for aircraft wherein the escape maneuver chiefly consists of adding full power and pitching the aircraft up to initiate a climb. This type of escape from grounding is not available to a surface vessel. U.S. Pat. No. 5,488,563 to Chazelle describes a ground proximity warning system for aircraft that suggests a turning maneuver to escape terrain. However, Chazelle does not disclose or suggest how such a system could be applied to ships, submarines or boats. U.S. Pat. No. 4,646,244 to Bateman discloses a terrain alerting methodology for submarines and aircraft. However, Bateman does not disclose terrain alerts for surface ships or terrain avoidance maneuvers.
The present invention includes recognition of the need to provide marine vessels with an alert of conditions that may lead to an inadvertent grounding and/or impact with obstacles in the vessel""s path. The alerts provided according to the present invention may be reactive and/or predictive alerts.
According to one aspect of the present invention, the ship""s sonar is utilized to provide an indication of impending impact with bottom obstructions based upon rate of change of water depth beneath the keel.
According to another aspect of the invention, a ocean bottom terrain data base is provided. The ship""s position and anticipated track are compared to the ocean bottom terrain data and an alert is provided when a hazardous condition is detected.
According to another aspect of the invention, the terrain database includes an obstruction or obstacle data base. The ship maximum height and anticipated track can be compared, for example, with the clearance height required under a bridge obstacle, and an alert provided to the crew if a collision hazard exists.
According to another aspect of the invention, ocean bottom hazards are displayed on a visual display representative of a plan view of the ocean or waterway bottom terrain. Preferably the terrain is displayed in various colors and/or dot pattern densities depending upon the degree of grounding hazard to the vessel and/or to the degree of obstacle collison hazard. In a preferred embodiment of the invention, the terrain that does not present a hazard to the vessel is displayed in a first color, terrain that is a potential hazard to the vessel is displayed as second color and terrain which represents an immediate and actual danger to the vessel is colored a third color.
More specifically, the bottom proximity awareness system comprises a navigational system configured to determine latitude, longitude, depth, point of intended movement, velocity, acceleration and/or speed of a vessel employing the system. The navigational system generates signals in response to the listed parameters. The system further comprises: a terrain database comprising depth data for underwater terrain and obstacle information as well as for port facilities; a processor configured to identify from the terrain database depth data within a range of the vessel; warning envelope generator; and a warning device. Further advantages and features of the present invention will be described in detail below.